1. Field of the Invention
This invention relates to a medical fluid-filled plastic container and several methods of making the same. More particularly, it relates to a medical fluid-filled plastic container in which, even if it is subjected to steam sterilization or stored for a long period of time, the medical fluid will not undergo deterioration, as well as several methods of making the same.
2. Description of the Prior Art
In the field of medical treatment, closed systems have recently come to be employed in the infusion of injectable fluids for the purpose of preventing the medical fluid from being exposed to the external environment. As infusion fluid containers for use in such closed systems, conventional glass bottles and glass ampules are being replaced by flexible plastic containers. In the case of such plastic containers, the infusion fluid is discharged under the action of gravity and the flexibility of the container material. This type of medical fluid-filled containers must have sufficient thermal resistance to withstand steam sterilization for the purpose of sterilizing their contents. Moreover, they are preferably formed of a transparent material so that their contents can be monitored from the outside.
Where the medical fluid within such a container contains a component subject to deterioration (such as oxidation) by oxygen, as in the case of highly concentrated amino acid solutions containing tryptophan, elemental diets (hereinafter referred to as EDs), fat emulsions for use by infusion, and infusion fluids containing antibiotics subject to oxidation or hydrolysis in the presence of oxygen, the presence of oxygen in the container or the medical fluid tends to cause deterioration or discoloration of the medical fluid.
Accordingly, it has been conventional practice to fill a plastic container with a medical fluid, replace the oxygen present in the container and the medical fluid by nitrogen gas, and then subject the resulting medical fluid-filled container to steam sterilization. However, it has been difficult to reliably remove the oxygen present in the container and the medical fluid by this method.
Moreover, most of the conventional plastic containers for medical fluids are formed of soft polyvinyl chloride. At ordinary temperatures, soft polyvinyl chloride has low permeability to oxygen gas, but its permeability to gases is still higher than that of glass bottles and glass ampules. Thus, such plastic containers have usually been packaged with a packaging material having good gas barrier properties. Nevertheless, deterioration or discoloration of the medical fluid has been unavoidable because the gas permeability of the packaging material increases during steam sterilization and because oxygen gradually passes through the packaging material and penetrates into the container during long-term storage.